K2: Strange behaviour during alignment and tests (part II)

[Hans Østnell]

 Hi group!

I have just finished the alignments and tests (part II) in my (second)
K2-project. Sofar all resistance checks are ok, and the results of the
alignment and tests have also been ok. Except for one thing: I think that
the AGC in the radio behaves rather strangely. It's pretty nervous in the
"Fast" position and switching to slow makes it a little bit better, but not
perfect. I have also noticed a "chuffing" or "clicking" sound in my
heaphones while tuning the radio aound on 40 metres. This sound (which
indeed is very difficult to describe) corresponds with the change of digits
on the display (regardless of tuning rate) and is very significant with the
appearance of a strong signal. Tuning the BC-band above 7100 KHz is very
annoying. The behaviour disappears when the antenna is disconnected, but
occours again when connecting a signal generator or other RF-source to the
antenna jack.

Measuring the AGC-treashold voltage on pin 5 of U2 (control board) gives a
range from 2.65-3.74 volts when adjusting R1 from counter-clockwise to
clockwise. The recommended voltage is 3.80 volts, which I never reach. I've
checked the control board very carefully, looking for solder bridges, cold
solderings, incorrect components etc, but everything seems to be fine. I've
even re-heated all solder joints on the control board without success.

Any ideas, anyone?

Regards,

Hans, LA2MOA
K2 #6341 - unfinished
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[David Woolley (E.L)]

  wrote:

> Measuring the AGC-treashold voltage on pin 5 of U2 (control board) gives a
> range from 2.65-3.74 volts when adjusting R1 from counter-clockwise to

This is normal, 3.8 is only achievable if all components have nominal
values (and may actually not even be achievable then). It might be worth
checking the 8V regulator voltage, though, as one person with a, bigger,
problem with the AGC reference had a regulator that was out of spec.


--
David Woolley
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